Retaining HIV-infected patients in care is critical to a successful response to HIV/AIDS in Africa, but loss to follow-up after enrollment often reaches 20%-40% by two years, placing millions of patients at risk of poor outcomes. A strategy to optimize retention within resource constraints is urgently needed, but must first overcome two critical challenges. First, lapses in retention may be due to psychological (e.g., stigma), structural (e.g., transportation) or systems (e.g., long waiting times) barriers Therefore, althoug three interventions have shown some efficacy for retention in randomized trials (SMS text messages, transport vouchers and peer navigators), each acts only on some barriers and is therefore is ineffectual for patients facing other barriers and is of limited overall effectivenessin real-world patient populations. Second, although poor retention is a crisis in Africa, most patients remain in care with minimal support. As a result, even the most effective of these interventions if applied uniformly as a one-size-fits-all approach will squander resources on patients who do not need help while helping only some patients in need. Sequential adaptive strategies - a novel class of public health approaches - may offer a solution to these challenges and simultaneously optimize both the effectiveness and efficiency of retention efforts. A candidate sequential adaptive strategy would start with a less expensive intervention (e.g., SMS) in all patients and then apply a more costly and intensive one (e.g., navigator) only to patients who show early signs of poor retention. Altering the initial intervention in response to a individual's behavior minimizes expenditures for patients for whom the initial intervention is sufficient (optimizing efficiency), but intensifies services for those who need additional or alternative help (optimizing effectiveness). We propose a sequential multiple assignment randomized trial to evaluate a family of such strategies. We will randomize 2,500 adults at six HIV clinics in Nyanza, Kenya to (1) standard of care routine education and counseling (REC), (2) SMS text messages, or (3) transport vouchers. Patients with early signs of weakening retention (defined as the first time a patient is 14 days late for an appointment) will be re-randomized to (1) a single episode of outreach (standard of care), (2) SMS combined with vouchers, or (3) a peer navigator. In Aim 1, we assess the comparative effectiveness of first-stage strategies (REC, SMS, voucher) to prevent lapses in retention. In Aim 2, we assess the comparative effectiveness of second stage strategies (outreach, SMS + voucher, navigator) to re-engage patients. Because the initial intervention changes both the numbers and types of patients who lapse and thereby the effect of any second intervention, in Aim 3 we assess the joint effectiveness and cost-effectiveness of sequenced prevention and re-engagement strategies. At study conclusion, our primary output will be a menu of adaptive strategies for retention, each accompanied by estimates of cost and effectiveness, which policy makers in different settings can use to advance the impact of HIV care and treatment programs in Africa.